A new bioenergy crop based on oil-rich seeds from the legume tree Pongamia pinnata

Peter M Gresshoff,¹ Latha Rangan,² Arief Indrasumunar,¹ Paul T Scott<sup>1

1</sup>Centre for Integrative Legume Research, School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Brisbane, QLD, Australia; ²Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Assam, India

Abstract: Any informed discussion on the future sources of energy in our world requires the consideration of renewable biofuels. These are produced by biological processes, such as plant growth based on photosynthesis and microbes using waste products from diverse origins. Many biofuels, such as ethanol produced from plants like sugarcane, are seen as sustainable, such paradigms should be critically analyzed in terms of total inputs. The legume tree Pongamia pinnata (also called Millettia pinnata) offers a substantiated opportunity for a sustainable biofuel feedstock. It is characterized by fast plant growth, broad tropical and subtropical growth habitat, and high annual yields of oil-rich seed. Annual yield of the seed-extracted oil, rich in the monounsaturated fatty acid oleic acid (C18:1), is between 1,000 and 5,000 L/ha, depending on local conditions, including rainfall, temperature, and soil. It can be burnt in bioenergy generators to yield electrical output. It can also be converted to biodiesel by transesterification for transportation and industrial use. Conversion to aviation jet fuel by hydrogenation and subsequent purification is also possible. The legume nature of the plant allows it to harbor nitrogen-fixing soil bacteria (broadly called “rhizobia”) in newly induced root organs called nodules. This symbiosis makes the energy inputs considerably less than those seen with nitrate fertilizer – requiring biofuel feedstocks, such as corn, sugarcane, and canola. Combined with general characteristics of plant, such as abundant seed set and large oil-rich seed, secondary products, such as seed meal and vigorous growth characteristics, make this tree an excellent candidate for sustainable bioenergy production in many parts of the globe.

Keywords: biofuel, biotechnology, legume, plant growth, renewables, sustainability